Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in acpi_scan_init()

David Hildenbrand
2019-07-25T13:05:08Z

On 25.07.19 14:56, Michal Hocko wrote:
> On Wed 24-07-19 16:30:17, David Hildenbrand wrote:
>> We end up calling __add_memory() without the device hotplug lock held.
>> (I used a local patch to assert in __add_memory() that the
>> device_hotplug_lock is held - I might upstream that as well soon)
>>
>> [ 26.771684] create_memory_block_devices+0xa4/0x140
>> [ 26.772952] add_memory_resource+0xde/0x200
>> [ 26.773987] __add_memory+0x6e/0xa0
>> [ 26.775161] acpi_memory_device_add+0x149/0x2b0
>> [ 26.776263] acpi_bus_attach+0xf1/0x1f0
>> [ 26.777247] acpi_bus_attach+0x66/0x1f0
>> [ 26.778268] acpi_bus_attach+0x66/0x1f0
>> [ 26.779073] acpi_bus_attach+0x66/0x1f0
>> [ 26.780143] acpi_bus_scan+0x3e/0x90
>> [ 26.780844] acpi_scan_init+0x109/0x257
>> [ 26.781638] acpi_init+0x2ab/0x30d
>> [ 26.782248] do_one_initcall+0x58/0x2cf
>> [ 26.783181] kernel_init_freeable+0x1bd/0x247
>> [ 26.784345] kernel_init+0x5/0xf1
>> [ 26.785314] ret_from_fork+0x3a/0x50
>>
>> So perform the locking just like in acpi_device_hotplug().
>
> While playing with the device_hotplug_lock, can we actually document
> what it is protecting please? I have a bad feeling that we are adding
> this lock just because some other code path does rather than with a good
> idea why it is needed. This patch just confirms that. What exactly does
> the lock protect from here in an early boot stage.

We have plenty of documentation already

mm/memory_hotplug.c

git grep -C5 device_hotplug mm/memory_hotplug.c

Also see

Documentation/core-api/memory-hotplug.rst

Regarding the early stage: primarily lockdep as I mentioned.

--

Thanks,

David / dhildenb